Abstract

The presence of trails and group size play a role in the biology of forest tent caterpillars ( Malacosoma disstria ). Therefore, the effect of the presence of trails and group size on caterpillar performance and behaviour were studied in a laboratory setting. Since forest tent caterpillars may undergo an ontogenetic shift from gregarious to solitary individuals as they mature, these effects were tested on second and fourth instar larvae. For this study, caterpillars were placed in environments with pre-laid trails and of different group sizes. Caterpillars were reared through a larval instar and their performance was measured at the end of the larval stage. Second instar larvae developed faster, and were smaller, when reared in the presence of trails and at larger group sizes. In contrast, fourth instar larvae did not show any differences in development rate. For behavioural observations, larvae were placed in similar environments to those in the performance experiments. The behaviour and foraging efficiency of caterpillars was monitored at regular intervals for four hours. For second instars, results suggest that differences in growth and development time in the presence of trails may be linked to foraging success. Young caterpillars are highly dependent on trails to locate their food while older ones are not. Behavioural observations show differences in frequency and duration of certain behaviours between second and fourth instar larvae. Changes in the performance and behaviour between larval stages suggest an ontogenetic shift may occur between second and fourth instars.